This invention relates to a position transducer for machine tools and measuring machines, realized by means of optical coupling of photoelectric readers and photoengraved rules in a new and particular arrangement.
At the present time, in the measuring machines and machine tools in which it is necessary to know with the best precision the position of a movable part, as for example a carriage, with respect to fixed reference positions, pinion/rack assemblies are used as position transducers. For example, the rack is fixed to the machine in a position parallel to the movement of the carriage, and meshing with the rack is a pinion pertaining to the carriage. As the carriage moves, the pinion rotates by an angle which is proportional to the displacement of the carriage. The resolution, and conseqently also the precision, obtained with this type of transducer is of about 1/100 of a millimeter. If it is desired to have a better resolution, in the order of one micron, transducers are utilized which are formed by an optical photoengraved rule and a photoelectric reader element. Said rule is a bar isostatically fixed to the structure of the machine in order that it will not be exposed to deformation, and having thin parallel equispaced traces formed thereon by means of photoengraving process. Said rules are of various lengths, but usually they are not constructed for lengths more than 3 meters, because greater lengths would involve problems of difficult thermal stabilization during the photoengraving process, as well as not negligible problems of transportation.
If the element on which the carriage slides is very long, for example five or more meters, it is impossible to use photoengraved rules and it is necessary to have recourse to the pinion/rack coupling, with consequent reduction of the resolution.